EPR INVESTIGATION OF PARAMAGNETIC SPECIES ON PALLADIUM-PROMOTED YTTRIA AND LANTHANA

Electron paramagnetic resonance studies have been carried out on Pd/Y2 O3 and Pd/La2O3 systems with low Pd loading. The samples were prepared by coprecipitation and by decomposition of amorphous citrate precurso rs. Oxidation of yttria-containing samples at 870 K leads to the forma tion of Pd3+, which converts into Pd+ on evacuation at 870 K, both spe cies being stabilized in the bulk. Mild reduction of doped yttria and lanthana in hydrogen gives another type of Pd+ ions localized within t he surface and subsurface layers. Formation of O-2(-) radical anions c oordinated with Y3+ or La3+ cations occurs readily at 77 K upon oxygen admission. The decay and formation of adsorbed radical anions is sens itive to the electron-donating properties of the sample (i.e. the surf ace concentration of Pd+).